Optical trapping has proved to be a valuable research tool in a wide range of fields including physics, chemistry and material science. The ability to place and manipulate individual colloidal particles in a precise three-dimensional location has been highly useful for the understanding of soft matter phenomena and inter-particle interactions. It also holds great promise for nanoscale fabrication and ultra-sensitive medium sensing by enabling precise positioning of specific material building blocks. An interesting consequence of optical trapping is seen when a large number of particles are trapped in a single holographic trap that is significantly larger than the particle diameter. Due to the interference effects between the incident light and scattered light, the particles become strongly bound to one another. This can lead to the creation of large, highly ordered structures of colloidal particles, termed optical matter. The geometry of the structure is dependent on the phase and polarization profile of the incident optical beam.
In this talk we discuss our research on the structural and dynamical effects on optical matter composed of plasmonic nanoparticles. We describe how the structures are formed from one particle up, and how their dynamics and structure are shaped by the size, phase profile, and polarization of the incident optical beam. Specifically we discuss how circular polarization can create an isotropic optical binding potential and induce rotation in the system, and how the rotation depends on the particle and beam characteristics.
Particle tracking is an important tool in a wide range of experimental fields in which optical imaging systems are used. Unfortunately, tracking algorithms are susceptible to pixel-locking when a tracked object occupies a small number of pixels on the detector or is near other particles, in which the particle localization is biased towards the pixel center. In this proceedings paper we demonstrate this effect and show how these errors can be ameliorated using the Single Pixel Interior Fill Function (SPIFF) algorithm, improving the fidelity of any metrics obtained from particle tracking (e.g interparticle separation). We analyze the severity of pixel bias inherent in optical systems of different magnification values and the effect that the SPIFF algorithm has on them. Our analysis demonstrates a tradeoff between the severity of the pixel locking and the signal-to-noise ratio of optical systems with different magnification.
Optical trapping has proved to be a valuable research tool in a wide range of fields including physics, chemistry, biological and materials science. The ability to precisely localize individual colloidal particles in a three-dimensional location has been highly useful for understanding soft matter phenomena and inter-particle interactions. It also holds great promise for nanoscale fabrication and ultra-sensitive sensing by enabling precise positioning of specific material building blocks. In this presentation we discuss our research on the effect of the polarization state of the incident laser on the trapping of nanoscale particles. The polarization of the incident light has a pronounced effect on particle behavior even for the simple case of two plasmonic silver nano-particles in a Gaussian trap,. When the incident light is linearly polarized, the particles form an optically induced dimer that is stably oriented along the direction of polarization. However, nanoparticle dimers and trimmers exhibit structural instabilities and novel dynamics when trapped with focused beams of circularly polarized light. The observed dynamics suggest electrodynamic and hydrodynamic coupling. We explore the electrodynamic phenomena experimentally and theoretically and discuss further examples of polarization controlled trapping.
We develop a new approach for obtaining wide-angle, broadband and efficient reflection holography by utilizing coupled dipole-patch nano-antenna cells to impose an arbitrary phase profile on of the reflected light. The holograms were projected at angles of 45° and 20° with respect to the impinging light with efficiencies ranging between 40%-50% over an optical bandwidth exceeding 180nm. Excellent agreement with the theoretical predictions was found at a wide spectral range. The demonstration of such reflectarrays opens new avenues towards expanding the limits of large angle holography.
We demonstrate a refractive index (RI) detection technique based on an array of nanometer scale slot-antennas milled in a thin gold layer using a single lithographic step. Our experimental Figures of merit (FOMs) of 140-210 in the telecom wavelength range approach the fundamental limit for standard propagating SPR sensors (~250). The underlying mechanism enabling such high FOMs is the combination of a narrowband resonance of the slot-antennas with degeneracy breaking of Wood’s anomaly under slightly non-perpendicular illumination. In addition, we study the sensitivity of the thickness of the analyte layer. This concept can be easily tuned to any desired wavelength and RI range by modifying the slot dimensions and the array spacing, thus rendering it highly attractive for numerous sensing applications.
We demonstrate the use of nano-antenna unit cells composed of coupled dipole and patch elements over a reflective back plane, which are designed to control the phase of a reflected optical beam. The antennas were studied both numerically and experimentally and allow exact control over the output phase in the range of 00-3600. Several diffractive optical applications are shown numerically and experimentally: Blazed gratings which allow deflection of the output beam to high reflection angles show very high diffraction efficiency, and arbitrary wave shapes such as computer generated holograms can be formed with very high efficiency and large angles relative to the incident beam. The optical conversion efficiency was measured to be above 40% for all applications.
We study the dynamics of coupled arrays of Vertical Cavity Surface Emitting Lasers (VCSELs) under optical injection
of light into on of the VCSEL in the array In spite of a theoretical expectation for slow light propagation exhibiting
resonance tunneling of the injected pulse to its adjacent lasers we observed the opposite effect - the light was first
observed in the VCSEL furthest away from the injection point. These rather surprising results are presented and several
possible explanations are discussed.
We study theoretically and experimentally the IR emission properties from gold nano-antenna arrays. A new
characterization method based on far field measurements only is developed and presented. Excellent agreement in terms
of resonance frequencies, optical bandwidth, and emission efficiency is found between the experimental results and a
theoretical analysis based on finite element modeling of the arrays. Extremely high overall emission efficiencies,
exceeding 95%, are obtained experimentally. The high efficiency and the simple far-field characterization scheme
presented here can facilitate the employment of such nano-antennas for numerous applications in imaging, spectroscopy,
and solar energy harvesting.
Slow light has been extensively studied in coupled arrays of passive optical resonators, and several applications have been demonstrated. We developed a theoretical framework for the design and analysis of arrays consisting of active resonators, in particular vertical cavity surface emitting lasers (VCESLs), which have potential applications as a flexible photonic platform. Building upon this framework, several such applications were analyzed for both one- and two-dimensional coupled VCSEL arrays. In particular, the use of two-dimensional VCSEL arrays holds great potential for several interesting applications such as tunable optical waveguides or optical splitters.
We propose a new scheme for manipulating optical information by trapping and releasing optical pulses propagating in
an array of coupled semiconductor lasers. The manipulation of the optical pulses is achieved directly by changing the
pump parameter of the individual lasers. Applications such as optical routing, delay lines and memories are studied in